Sheet feed detecting devices



D. BROIDO July 26, 1960 V SHEET FEED DETECTING DEVICES Filed July 31, 1956 il'k INVENTQR flaw 1. BRO/D0 BY MW ATTORN EY United States Patent SHEET-FEED DETECTING DEVICES Daniel Broido, Cockfosters, near Barnet, England, assignor to International Computers and Tabulators Limited, London, England, a Britishcompany Filed July 31, 1956, Ser. No. 601,190 v Claims priority, application Great Britain Oct. 11, 1955 12 Claims. (Cl. 340-259 The present invention, relates to sheet feeding mechanisms and is particularly concerned with arrangements for detecting the departure from predetermined spacing of sheets moving along a feed path. r

The invention is applicable to machines for feeding paper documents, punched cards and the like, in which it is desirable to check the spacing between successive documents without impeding free movement of such documents along the feed path, as, for example, in the machine for sorting documents described in United States patent -ap plication No. 532,951 filed September 7, 1955. 7

It will be appreciated that in the event of one of a series of documents being arrested succeeding documents will tend to pile up about the obstruction caused by the ar-,

soon as possible. Moreover in certain types of machine,

such as sorting machines, the correct performance of an operation upon a document travelling along a feed path may depend upon the delivery of such document to a particular point in the path at a particular instant. Under such circumstances displacement of the document from its correct path and time of movement may result in incorrect operation of the machine, or even in a document being arrested so as to result in a pile-up of succeeding documents.

The most convenient method of checking the correct relative positioning of closely spaced documents fed along a path is by checking the spacing between documents, so that any tendency towards incorrect positioning is detected and alarm and control action initiated before serious misoperation or pile-up actually occurs.

It is the object of the invention to achieve this result in a manner which does not involve any physical contacting of the documents which might itself give rise to incorrect relative positioning of the documents.

According to the invention apparatus for detecting incorrect feeding of sheets along a feed path has one or more photo-electric cells mounted in fixed positions relative to the feed path, a single output circuit for said cell or cells, means for illuminating said cell or cells in such a way that a change in the signal from the output circuit is produced by an error in the position of any one of two .or more sheets along the feed path, and error indicating means operable by the output signal to initiate alarm and/ or control action if incorrect feeding occurs. The error indicating means may be made effective at predetermined intervals under control of a timing device.

The invention will now be described, by way of example, as appliedto the document sorting machine described in the aforesaid patent application No. 532,951, with reference to the accompanying drawing, in which:

Figure 1 illustrates schematically a document sorting machine.

Figure 2 shows the optical arrangements of Figure 1 in greater detail. c

Figure 3 shows an error indicating circuit;

Patented July 2o, 1960 No. 532,951 to which reference is made for detailed description of the construction and operation of the machine itself. Briefly, in such a machine documents are fed from the'le'ft hand sideof the machine (as shown) past the sensing head 1 along a feeding path lying over the sorting pockets 2. 'The entry flaps 3 of such pockets are selectively opened in dependence upon the output of the sensing head 1 by the mechanism indicated at 4 so that the documents are diverted into appropriate pockets as they travel along the feeding path.

The detecting arrangement is shown mounted above the feeding path'in Figure 1. It comprises three light sources 5a, 5b and 5c, three vertical mirrors 6a, 6b and 6c, a horizontal mirror 7 and a photo-electric cell 8. The details of this arrangement can best be seen from Figure 2 in which the feed plate over which the documents are fed is indicated at 9 and the individual documents at 10. Referring to Figure 2, individual beams from the light sources 5 impinge first upon the highly polished upper surface of the run 9 and are separately reflected on to the horizontal mirror 7 and thence back to the surface of the run 9 and so on. The beams finally emerge to impinge on the vertical mirrors 6 which are arranged to reflect all the beams on to the photo-cell 8.

The angles of the impinging beams are so arranged that the points at which such beams impinge on the plate 9 are spaced apart by the correct spacing distance of the documents 10'. There is a point in each document feeding cycle when all the beams impinge on the spaces between the documents, provided the documents are correctly spaced, and the maximum intensity of reflected light is received by the photocell 8. By a cam-operated switching device, similar to the switch 23 of Figure 5, the potential developed by the current through cell 8 is switched to an error indicating unit (Figure 3) at successive instants of maximum light, in synchronism with the document feeding operations. 1

If one of the documents is displaced from its correct position relative to other documents travelling along the feed path, the amount of light reflected will be reduced, since the displaced document will obscure a normal reflecting point on the plate 9. There is thus an increase in the potential developed across the cell 8.

The use of several beams of light has two advantages. Firstly, each beam suffers fewer reflections, so that there is a greater tolerance in the reflecting properties of the surfaces of the plate 9 and the mirror 10. Secondly, it

' flection appropriately, it can be ensured that at a fixed time in the feeding cycle at least one beam will be reflected to the photo-cell if the sheets are being fed correctly.

The modified arrangement of Figure 4 employs individual photo-cells which are spaced apart by a multiple of the distance between documents. In Figure 4, four light sources 5d, 5e, 5 and 5g are shown mounted verticallyso as to direct light beams downwardly through apertures 17d, 17e, 17 and 17g on to photocells 18d, 18c, 18 and 18g respectively.

As with the preceding embodiment, when a document interrupts a light beam at a time when the beam should pass throughthe space between two documents, the potential developed by the current through the corresponding cell rises and a signal is passed to the error indicating unit.

The circuit connections of. the cells 18 are shown in Figure 5, from which it will be seen that each cell, with its. load resistor, 19 is connected in a parallel arm. of a network, the junction between the cell and the load in each case being connected via a diode 24 to the moving contact of a cam-operated switch, 23., The stationary contact of the switch 23 is connected through capacitor 22 to line 25 which leads to the error indicating unit of Figure 3, and is also connected through resistor 20 to the junction between a balancing photo-cell 18x, illuminated by source x, and its load resistor 19x. A resistor 21 is inserted between the cell 18x and such junction point. The stationary contact and the line 25. thus carry a steady potential applied by the cell 182:, and this is arranged by the provision of the resistor 21 to be slightly greater than the potential picked up by the stationary contact from the moving contact upon operation of the switch during normal running of the machine. When however, one of the cells ISd-g is obscured by a displaced document the potential picked up from the moving contact is considerably higher than that normally present on the stationary contact so that a positive going pulse is fed to the line 25.

The arrangement of the switch 23 and balancing photo-cell 18x is also used with the embodiment of Figure 2 in order to apply a reasonably constant potential to the error indicating unit during normal running of the machine. The light source Ex is connected to the same voltage supply as the other sources, so that variations in the voltage supplies to either the light sources or the cells have less effect on the operation of the circuit.

The error indicating unit (Figure 3) comprises a normally non-conducting thyratron TI-Il having a relay 26 in its anode circuit and a control grid circuit including resistors 27 and 28 to which the line 25 is connected. A capacitor 29 between the control grid and earth serves, in conjunction with resistor 28, as an integrating circuit to prevent tiring of the thyratron by spurious positive pulses of short duration compared to the pulse from the cells. The positive-going voltage pulse, developed when a document is displaced, is applied over lead 25 to fire the thyratron THl, and the resultant anode current operates the relay 26. The contacts of the relay 2.6 may break the circuit to an electromagnct which control a clutch driving the feed mechanism {911:1 example, or they may complete circuit to a Warning It will be appreciated that the error indicating unit may also control stopping of the machine in response to signals from other sources, for example from manually operated switches provided for use by the machine operator, or from an arrangement for detecting superimposed documents.

What I claim is:

1. Apparatus for detecting incorrect positioning of sheets moved along a feed path and spaced apart along the feed path at nominally regular intervals, said apparatus comprising detecting means including photoelectric means, means for directing a plurality of light beams on to the photo-electric means through paths intersecting said feed path, said light beams intersecting said feed path at a plurality of points spaced along its length by intervals each of which is an integral multiple of the correct spacing of successive sheets and each beam being interrupted when any part of a sheet coincides with the corresponding one of said spaced points, means for deriving an output signal from the photoelectric means indicative at any instant of the interruption of any of said light beams, error indicating means controlled by said output signal to initiate a control action in response to said output signal being indicative of the interruption of any one of said light beams, and timing means synchronised with the motion of said sheets for rendering the error indicating means effective only during those periods when, if the spacing of the sheets is correct, spaces between the sheets traverse said spaced points on said feed path.

2. Apparatus as claimed in claim 1 in which said light directing means includes a plurality of light sources, a separate one for each beam.

3. Apparatus as claimed in claim 1 in which said feed path has a light reflecting surface on which said sheets lie when traversing said feed path and said photo-electric means is positioned to receive said light beams after intersection of said feed path and reflection from said light-reflecting surface.

4. Apparatus as claimed in claim 3 in which said photo-electric means includes a single photo-electric cell and the apparatus further includes mirrors for reflecting all said light beams on to the single cell.

5. Apparatus as claimed in claim 3 which further includes a fixed body having a reflecting surface which is parallel to and directed towards the reflecting surface of said feed path but lies on the opposite side of said feed path to the latter reflecting surface, and said light beams when first incident on the latter reflecting surface are all parallel, the spacing between the two reflecting surfaces being related to the angle of incidence of said light beams on the reflecting surface of said feed path and the correct spacing of successive sheets to cause each beam to undergo multiple reflection and intersect said feed path at a plurality of points spaced apart from one another by an integral multiple of said correct spacing.

6. Apparatus as claimed in claim 1 in which said feed path is provided with apertures, location of said apertures within the spaces between adjacent sheets being indicative of a correct spacing of the sheets, said light directing means directs said beams to intersect said feed path at a point lying over the line of travel of said apertures, and the photo-electric means is positioned to receive said light beams after intersection of said feed path and traversal of said apertures.

7. Apparatus as claimed in claim 6 in which said light directing means includes a plurality of light sources each positioned to direct a beam vertically downwards to intersect said feed path.

8. Apparatus as claimed in claim 7 in which the photo-electric means includes a plurality of photo-electric cells positioned one vertically beneath each of said plurality of light sources on the side of said feed path remote from said sources.

9. Apparatus as claimed in claim 1 and further including a further photo-electric means continuously operable .to produce a standard signal, means for applying said standard signal to said error indicating means to maintain it in a quiescent condition and means for comparing said standard and said output signals and for causing said error indicating means to initiate a control action when said output signal indicates the in terruption of one of said light beams.

10. Apparatus as claimed in claim 9 in which said error indicating means includes a gas-filled thermionic valve connected in a circuit such that it is normally nonconduoting, said comparison means includes means for causing the application of a pulse to fire said valve when said output signal indicates the interruption of one of said light beams, and said error indicating means further includes relay means connected to be energised by current flowing through said valve.

11. Apparatus as claimed in claim 9 in which said timing means includes switch means having a contact connected in said comparison means to prevent comparison of said output signal with said standard signal except when spaces between the sheets should traverse said spaced points on said feed path.

12. Apparatus including a mechanism for feeding sheets along a feed path at nominally regular intervals 5 and means for detecting incorrect spacing of the sheets along said feed path, said detecting means including photo-electric means, means for directing a plurality of light beams on to the photoelectric means through paths intersecting said feed path, said light beams intersecting said feed path at a plunality of points spaced along its length by intervals each of which is an integnal multiple of the correct spacing of successive sheets and each beam being interrupted when any part of a sheet coincides with the corresponding one of said spaced points, means for deriving an output signal from the photo-electric means indicative at any instant of the in temiption of any of said light beams, error indicating means controlled by said output signal to initiate a control action in response to said output signal being in- 15 2,

6 dicative of the interruption of any one of said light beams, and timing means synchronized with said sheet feeding mechanism for rendering the error indicating means eifective only during those periods when, if the spacing of the sheets is correct, spaces between the sheets traverse said spaced points on said feed path.

References Cited in the file of this patent UNITED STATES PATENTS 2,183,606 Day Dec. 19, 1939 2,289,737 Sorkin July 14, 1942 2,451,816 Dunn Oct. 19, 1949 Hangartner Dec. 7, 1954 Gulliksen Aug. 29, 1939 

